Retrograde memory after unilateral stroke

Over the past two decades, there has been a growing interest in understanding the neural underpinnings of memory of the past. Numerous patients with retrograde amnesia after acute brain damage have been described, but often the causative lesions are bilateral and/or fairly diffuse and one question that has arisen is whether a unilateral lesion is sufficient to cause retrograde memory impairment. In addition, the impact of lesion side and site on the material specificity and temporal extent of retrograde memory deficits has remained unclear. We set out to investigate these issues by comparing 20 patients who had recently had a unilateral stroke that involved (but was not necessarily limited to) either the frontal or temporal lobe to a group of 10 matched normal control subjects on tests of memory of events and semantic details from the autobiographical and public domains. Results indicated that a unilateral lesion was sufficient to cause significant retrograde memory impairment, with right-sided lesions affecting recall of autobiographical events more than left-sided lesions. The memory deficits in these patients were most often relatively mild, but temporally pervasive rather than characterised by a traditional temporal gradient. Furthermore, memory of events (both autobiographical and public) was impaired in patients who had had a stroke that included the hippocampus, but not in those whose strokes spared this region. Finding that patients with mesial temporal lesions had difficulty remembering details related to public events, even when offered recognition choices, raises the possibility that part of their memory storage network (and not just their retrieval abilities) was compromised.